In general, indoor lighting apparatuses using LEDs may be divided into apparatuses of a bulb type that replace typical bulbs, and surface-lighting apparatuses that replace fluorescent lamps.
Most of the surface-lighting apparatuses adopt a diffusion plate of a specific area as shown in Korea Patent No. 10-0998980 (registered on 1 Dec. 2010). The Patent discloses a configuration that includes a substrate having a plurality of LEDs for emitting light upwards mounted thereon, and at least one diffusion layer on the surface of the substrate, such that the light emitted from the plurality of LEDs is diffused to illuminate the entire surface of a specific area at a uniform intensity of illumination, as shown in the primary drawing, i.e., FIG. 4.
Such a configuration is usually adopted by the typical surface-lighting apparatuses, wherein the diffusion plate can prevent the light from emitting intensively from a specific portion to thereby eliminate the dazzle of a light, but the light-efficiency is lowered due to a significant light loss.
Accordingly, a multitude of LEDs, more than are needed, need to be used in order to provide a surface-lighting source that has a sufficient intensity of illumination. This may cause the strength of LED lights, i.e., low electric power consumption, to be useless. In addition, since it is not easy to deal with the heat emitted from the LEDs, the LED life-span may be shortened due to the heat.
Moreover, in the surface-lighting apparatus illustrated in FIG. 4 of the Patent above, if a typical lighting apparatus of 40 W is designed to be altered to a lighting apparatus of 20 W using LED chips of the same electric power, the design of a case should be changed.
In this case, the number of LEDs used in the lighting apparatus of 20 W is only half the number of LEDs used in the lighting apparatus of 40 W, so the gap between the LEDs become bigger due to the decrease in the number of LEDs. Accordingly, the diffusion plate just below the light-emitting surface of the LEDs shows bright portions and dark portions, which cause uneven illumination on the light-emitting surface.
In order to eliminate the unevenness of illumination, the distance between the LEDs and the diffusion plate should be adjusted to be longer through the change of the design. Alternatively, while the size of the light-emitting unit is to be reduced by half, another half of the light-emitting unit should be replaced with a reflection plate.